2 % (c) The University of Glasgow 2006
3 % (c) The GRASP Project, Glasgow University, 1992-2002
7 TcRnIf, TcRn, TcM, RnM, IfM, IfL, IfG, -- The monad is opaque outside this module
10 -- The environment types
12 TcGblEnv(..), TcLclEnv(..),
13 IfGblEnv(..), IfLclEnv(..),
16 ErrCtxt, RecFieldEnv(..),
17 ImportAvails(..), emptyImportAvails, plusImportAvails,
18 WhereFrom(..), mkModDeps,
21 TcTypeEnv, TcTyThing(..), pprTcTyThingCategory,
24 ThStage(..), topStage, topAnnStage, topSpliceStage,
25 ThLevel, impLevel, outerLevel, thLevel,
28 ArrowCtxt(NoArrowCtxt), newArrowScope, escapeArrowScope,
31 Untouchables(..), inTouchableRange, isNoUntouchables,
33 WantedConstraints(..), insolubleWC, emptyWC, isEmptyWC,
34 andWC, addFlats, addImplics, mkFlatWC,
36 EvVarX(..), mkEvVarX, evVarOf, evVarX, evVarOfPred,
37 WantedEvVar, wantedToFlavored,
41 CtLoc(..), ctLocSpan, ctLocOrigin, setCtLocOrigin,
42 CtOrigin(..), EqOrigin(..),
43 WantedLoc, GivenLoc, pushErrCtxt,
47 CtFlavor(..), pprFlavorArising, isWanted, isGiven, isDerived,
51 pprEvVarTheta, pprWantedEvVar, pprWantedsWithLocs,
52 pprEvVars, pprEvVarWithType,
53 pprArising, pprArisingAt,
56 TcId, TcIdSet, TcTyVarBind(..), TcTyVarBinds
60 #include "HsVersions.h"
65 import Class ( Class )
66 import DataCon ( DataCon, dataConUserType )
95 %************************************************************************
97 Standard monad definition for TcRn
98 All the combinators for the monad can be found in TcRnMonad
100 %************************************************************************
102 The monad itself has to be defined here, because it is mentioned by ErrCtxt
105 type TcRef a = IORef a
106 type TcId = Id -- Type may be a TcType DV: WHAT??????????
110 type TcRnIf a b c = IOEnv (Env a b) c
111 type IfM lcl a = TcRnIf IfGblEnv lcl a -- Iface stuff
113 type IfG a = IfM () a -- Top level
114 type IfL a = IfM IfLclEnv a -- Nested
115 type TcRn a = TcRnIf TcGblEnv TcLclEnv a
116 type RnM a = TcRn a -- Historical
117 type TcM a = TcRn a -- Historical
120 Representation of type bindings to uninstantiated meta variables used during
124 data TcTyVarBind = TcTyVarBind TcTyVar TcType
126 type TcTyVarBinds = Bag TcTyVarBind
128 instance Outputable TcTyVarBind where
129 ppr (TcTyVarBind tv ty) = ppr tv <+> text ":=" <+> ppr ty
133 %************************************************************************
135 The main environment types
137 %************************************************************************
140 data Env gbl lcl -- Changes as we move into an expression
142 env_top :: HscEnv, -- Top-level stuff that never changes
143 -- Includes all info about imported things
145 env_us :: {-# UNPACK #-} !(IORef UniqSupply),
146 -- Unique supply for local varibles
148 env_gbl :: gbl, -- Info about things defined at the top level
149 -- of the module being compiled
151 env_lcl :: lcl -- Nested stuff; changes as we go into
154 -- TcGblEnv describes the top-level of the module at the
155 -- point at which the typechecker is finished work.
156 -- It is this structure that is handed on to the desugarer
160 tcg_mod :: Module, -- ^ Module being compiled
161 tcg_src :: HscSource,
162 -- ^ What kind of module (regular Haskell, hs-boot, ext-core)
164 tcg_rdr_env :: GlobalRdrEnv, -- ^ Top level envt; used during renaming
165 tcg_default :: Maybe [Type],
166 -- ^ Types used for defaulting. @Nothing@ => no @default@ decl
168 tcg_fix_env :: FixityEnv, -- ^ Just for things in this module
169 tcg_field_env :: RecFieldEnv, -- ^ Just for things in this module
171 tcg_type_env :: TypeEnv,
172 -- ^ Global type env for the module we are compiling now. All
173 -- TyCons and Classes (for this module) end up in here right away,
174 -- along with their derived constructors, selectors.
176 -- (Ids defined in this module start in the local envt, though they
177 -- move to the global envt during zonking)
179 tcg_type_env_var :: TcRef TypeEnv,
180 -- Used only to initialise the interface-file
181 -- typechecker in initIfaceTcRn, so that it can see stuff
182 -- bound in this module when dealing with hi-boot recursions
183 -- Updated at intervals (e.g. after dealing with types and classes)
185 tcg_inst_env :: InstEnv,
186 -- ^ Instance envt for /home-package/ modules; Includes the dfuns in
188 tcg_fam_inst_env :: FamInstEnv, -- ^ Ditto for family instances
190 -- Now a bunch of things about this module that are simply
191 -- accumulated, but never consulted until the end.
192 -- Nevertheless, it's convenient to accumulate them along
193 -- with the rest of the info from this module.
194 tcg_exports :: [AvailInfo], -- ^ What is exported
195 tcg_imports :: ImportAvails,
196 -- ^ Information about what was imported from where, including
197 -- things bound in this module.
200 -- ^ What is defined in this module and what is used.
201 -- The latter is used to generate
203 -- (a) version tracking; no need to recompile if these things have
204 -- not changed version stamp
206 -- (b) unused-import info
208 tcg_keep :: TcRef NameSet,
209 -- ^ Locally-defined top-level names to keep alive.
211 -- "Keep alive" means give them an Exported flag, so that the
212 -- simplifier does not discard them as dead code, and so that they
213 -- are exposed in the interface file (but not to export to the
216 -- Some things, like dict-fun Ids and default-method Ids are "born"
217 -- with the Exported flag on, for exactly the above reason, but some
218 -- we only discover as we go. Specifically:
220 -- * The to/from functions for generic data types
222 -- * Top-level variables appearing free in the RHS of an orphan
225 -- * Top-level variables appearing free in a TH bracket
227 tcg_th_used :: TcRef Bool,
228 -- ^ @True@ <=> Template Haskell syntax used.
230 -- We need this so that we can generate a dependency on the
231 -- Template Haskell package, becuase the desugarer is going
232 -- to emit loads of references to TH symbols. The reference
233 -- is implicit rather than explicit, so we have to zap a
236 tcg_dfun_n :: TcRef OccSet,
237 -- ^ Allows us to choose unique DFun names.
239 -- The next fields accumulate the payload of the module
240 -- The binds, rules and foreign-decl fiels are collected
241 -- initially in un-zonked form and are finally zonked in tcRnSrcDecls
243 tcg_rn_exports :: Maybe [Located (IE Name)],
244 tcg_rn_imports :: [LImportDecl Name],
245 -- Keep the renamed imports regardless. They are not
246 -- voluminous and are needed if you want to report unused imports
248 tcg_used_rdrnames :: TcRef (Set RdrName),
249 -- The set of used *imported* (not locally-defined) RdrNames
250 -- Used only to report unused import declarations
252 tcg_rn_decls :: Maybe (HsGroup Name),
253 -- ^ Renamed decls, maybe. @Nothing@ <=> Don't retain renamed
256 tcg_ev_binds :: Bag EvBind, -- Top-level evidence bindings
257 tcg_binds :: LHsBinds Id, -- Value bindings in this module
258 tcg_sigs :: NameSet, -- ...Top-level names that *lack* a signature
259 tcg_imp_specs :: [LTcSpecPrag], -- ...SPECIALISE prags for imported Ids
260 tcg_warns :: Warnings, -- ...Warnings and deprecations
261 tcg_anns :: [Annotation], -- ...Annotations
262 tcg_insts :: [Instance], -- ...Instances
263 tcg_fam_insts :: [FamInst], -- ...Family instances
264 tcg_rules :: [LRuleDecl Id], -- ...Rules
265 tcg_fords :: [LForeignDecl Id], -- ...Foreign import & exports
266 tcg_vects :: [LVectDecl Id], -- ...Vectorisation declarations
268 tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
269 tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the
270 -- prog uses hpc instrumentation.
272 tcg_main :: Maybe Name -- ^ The Name of the main
273 -- function, if this module is
278 = RecFields (NameEnv [Name]) -- Maps a constructor name *in this module*
279 -- to the fields for that constructor
280 NameSet -- Set of all fields declared *in this module*;
281 -- used to suppress name-shadowing complaints
282 -- when using record wild cards
283 -- E.g. let fld = e in C {..}
284 -- This is used when dealing with ".." notation in record
285 -- construction and pattern matching.
286 -- The FieldEnv deals *only* with constructors defined in *this*
287 -- module. For imported modules, we get the same info from the
291 %************************************************************************
293 The interface environments
294 Used when dealing with IfaceDecls
296 %************************************************************************
301 -- The type environment for the module being compiled,
302 -- in case the interface refers back to it via a reference that
303 -- was originally a hi-boot file.
304 -- We need the module name so we can test when it's appropriate
305 -- to look in this env.
306 if_rec_types :: Maybe (Module, IfG TypeEnv)
307 -- Allows a read effect, so it can be in a mutable
308 -- variable; c.f. handling the external package type env
309 -- Nothing => interactive stuff, no loops possible
314 -- The module for the current IfaceDecl
315 -- So if we see f = \x -> x
316 -- it means M.f = \x -> x, where M is the if_mod
319 -- The field is used only for error reporting
320 -- if (say) there's a Lint error in it
322 -- Where the interface came from:
323 -- .hi file, or GHCi state, or ext core
324 -- plus which bit is currently being examined
326 if_tv_env :: UniqFM TyVar, -- Nested tyvar bindings
327 if_id_env :: UniqFM Id -- Nested id binding
332 %************************************************************************
334 The local typechecker environment
336 %************************************************************************
338 The Global-Env/Local-Env story
339 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
340 During type checking, we keep in the tcg_type_env
341 * All types and classes
342 * All Ids derived from types and classes (constructors, selectors)
344 At the end of type checking, we zonk the local bindings,
345 and as we do so we add to the tcg_type_env
346 * Locally defined top-level Ids
348 Why? Because they are now Ids not TcIds. This final GlobalEnv is
349 a) fed back (via the knot) to typechecking the
350 unfoldings of interface signatures
351 b) used in the ModDetails of this module
354 data TcLclEnv -- Changes as we move inside an expression
355 -- Discarded after typecheck/rename; not passed on to desugarer
357 tcl_loc :: SrcSpan, -- Source span
358 tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top
359 tcl_errs :: TcRef Messages, -- Place to accumulate errors
361 tcl_th_ctxt :: ThStage, -- Template Haskell context
362 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
364 tcl_rdr :: LocalRdrEnv, -- Local name envt
365 -- Maintained during renaming, of course, but also during
366 -- type checking, solely so that when renaming a Template-Haskell
367 -- splice we have the right environment for the renamer.
369 -- Does *not* include global name envt; may shadow it
370 -- Includes both ordinary variables and type variables;
371 -- they are kept distinct because tyvar have a different
372 -- occurrence contructor (Name.TvOcc)
373 -- We still need the unsullied global name env so that
374 -- we can look up record field names
376 tcl_hetMetLevel :: [TyVar], -- The current environment classifier level (list-of-names)
377 tcl_env :: TcTypeEnv, -- The local type environment: Ids and
378 -- TyVars defined in this module
380 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
381 -- Namely, the in-scope TyVars bound in tcl_env,
382 -- plus the tyvars mentioned in the types of Ids bound
384 -- Why mutable? see notes with tcGetGlobalTyVars
386 tcl_lie :: TcRef WantedConstraints, -- Place to accumulate type constraints
389 tcl_meta :: TcRef Unique, -- The next free unique for TcMetaTyVars
390 -- Guaranteed to be allocated linearly
391 tcl_untch :: Unique -- Any TcMetaTyVar with
392 -- unique >= tcl_untch is touchable
393 -- unique < tcl_untch is untouchable
396 type TcTypeEnv = NameEnv TcTyThing
399 {- Note [Given Insts]
401 Because of GADTs, we have to pass inwards the Insts provided by type signatures
402 and existential contexts. Consider
403 data T a where { T1 :: b -> b -> T [b] }
404 f :: Eq a => T a -> Bool
405 f (T1 x y) = [x]==[y]
407 The constructor T1 binds an existential variable 'b', and we need Eq [b].
408 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
413 ---------------------------
414 -- Template Haskell stages and levels
415 ---------------------------
417 data ThStage -- See Note [Template Haskell state diagram] in TcSplice
418 = Splice -- Top-level splicing
419 -- This code will be run *at compile time*;
420 -- the result replaces the splice
423 | Comp -- Ordinary Haskell code
426 | Brack -- Inside brackets
427 ThStage -- Binding level = level(stage) + 1
428 (TcRef [PendingSplice]) -- Accumulate pending splices here
429 (TcRef WantedConstraints) -- and type constraints here
431 topStage, topAnnStage, topSpliceStage :: ThStage
434 topSpliceStage = Splice
436 instance Outputable ThStage where
437 ppr Splice = text "Splice"
438 ppr Comp = text "Comp"
439 ppr (Brack s _ _) = text "Brack" <> parens (ppr s)
442 -- See Note [Template Haskell levels] in TcSplice
443 -- Incremented when going inside a bracket,
444 -- decremented when going inside a splice
445 -- NB: ThLevel is one greater than the 'n' in Fig 2 of the
446 -- original "Template meta-programming for Haskell" paper
448 impLevel, outerLevel :: ThLevel
449 impLevel = 0 -- Imported things; they can be used inside a top level splice
450 outerLevel = 1 -- Things defined outside brackets
451 -- NB: Things at level 0 are not *necessarily* imported.
452 -- eg $( \b -> ... ) here b is bound at level 0
456 -- g1 = $(map ...) is OK
457 -- g2 = $(f ...) is not OK; because we havn't compiled f yet
459 thLevel :: ThStage -> ThLevel
462 thLevel (Brack s _ _) = thLevel s + 1
464 ---------------------------
465 -- Arrow-notation context
466 ---------------------------
469 In arrow notation, a variable bound by a proc (or enclosed let/kappa)
470 is not in scope to the left of an arrow tail (-<) or the head of (|..|).
475 Here, x is not in scope in e1, but it is in scope in e2. This can get
479 proc y -> (proc z -> e1) -< e2
481 Here, x and z are in scope in e1, but y is not. We implement this by
482 recording the environment when passing a proc (using newArrowScope),
483 and returning to that (using escapeArrowScope) on the left of -< and the
489 | ArrowCtxt (Env TcGblEnv TcLclEnv)
491 -- Record the current environment (outside a proc)
492 newArrowScope :: TcM a -> TcM a
495 env { env_lcl = (env_lcl env) { tcl_arrow_ctxt = ArrowCtxt env } }
497 -- Return to the stored environment (from the enclosing proc)
498 escapeArrowScope :: TcM a -> TcM a
500 = updEnv $ \ env -> case tcl_arrow_ctxt (env_lcl env) of
502 ArrowCtxt env' -> env'
504 ---------------------------
506 ---------------------------
509 = AGlobal TyThing -- Used only in the return type of a lookup
511 | ATcId { -- Ids defined in this module; may not be fully zonked
513 tct_level :: ThLevel,
514 tct_hetMetLevel :: [TyVar]
517 | ATyVar Name TcType -- The type to which the lexically scoped type vaiable
518 -- is currently refined. We only need the Name
519 -- for error-message purposes; it is the corresponding
520 -- Name in the domain of the envt
522 | AThing TcKind -- Used temporarily, during kind checking, for the
523 -- tycons and clases in this recursive group
525 instance Outputable TcTyThing where -- Debugging only
526 ppr (AGlobal g) = pprTyThing g
527 ppr elt@(ATcId {}) = text "Identifier" <>
528 brackets (ppr (tct_id elt) <> dcolon
529 <> ppr (varType (tct_id elt)) <> comma
530 <+> ppr (tct_level elt)
531 <+> ppr (tct_hetMetLevel elt))
532 ppr (ATyVar tv _) = text "Type variable" <+> quotes (ppr tv)
533 ppr (AThing k) = text "AThing" <+> ppr k
535 pprTcTyThingCategory :: TcTyThing -> SDoc
536 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
537 pprTcTyThingCategory (ATyVar {}) = ptext (sLit "Type variable")
538 pprTcTyThingCategory (ATcId {}) = ptext (sLit "Local identifier")
539 pprTcTyThingCategory (AThing {}) = ptext (sLit "Kinded thing")
543 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, Message))
544 -- Monadic so that we have a chance
545 -- to deal with bound type variables just before error
546 -- message construction
548 -- Bool: True <=> this is a landmark context; do not
549 -- discard it when trimming for display
553 %************************************************************************
555 Operations over ImportAvails
557 %************************************************************************
560 -- | 'ImportAvails' summarises what was imported from where, irrespective of
561 -- whether the imported things are actually used or not. It is used:
563 -- * when processing the export list,
565 -- * when constructing usage info for the interface file,
567 -- * to identify the list of directly imported modules for initialisation
568 -- purposes and for optimised overlap checking of family instances,
570 -- * when figuring out what things are really unused
574 imp_mods :: ModuleEnv [(ModuleName, Bool, SrcSpan)],
575 -- ^ Domain is all directly-imported modules
576 -- The 'ModuleName' is what the module was imported as, e.g. in
584 -- - @True@ => import was @import Foo ()@
586 -- - @False@ => import was some other form
590 -- (a) to help construct the usage information in the interface
591 -- file; if we import somethign we need to recompile if the
592 -- export version changes
594 -- (b) to specify what child modules to initialise
596 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
597 -- because we might be importing modules of the same name from
598 -- different packages. (currently not the case, but might be in the
601 imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface),
602 -- ^ Home-package modules needed by the module being compiled
604 -- It doesn't matter whether any of these dependencies
605 -- are actually /used/ when compiling the module; they
606 -- are listed if they are below it at all. For
607 -- example, suppose M imports A which imports X. Then
608 -- compiling M might not need to consult X.hi, but X
609 -- is still listed in M's dependencies.
611 imp_dep_pkgs :: [PackageId],
612 -- ^ Packages needed by the module being compiled, whether directly,
613 -- or via other modules in this package, or via modules imported
614 -- from other packages.
616 imp_orphs :: [Module],
617 -- ^ Orphan modules below us in the import tree (and maybe including
618 -- us for imported modules)
620 imp_finsts :: [Module]
621 -- ^ Family instance modules below us in the import tree (and maybe
622 -- including us for imported modules)
625 mkModDeps :: [(ModuleName, IsBootInterface)]
626 -> ModuleNameEnv (ModuleName, IsBootInterface)
627 mkModDeps deps = foldl add emptyUFM deps
629 add env elt@(m,_) = addToUFM env m elt
631 emptyImportAvails :: ImportAvails
632 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
633 imp_dep_mods = emptyUFM,
638 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
640 (ImportAvails { imp_mods = mods1,
641 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
642 imp_orphs = orphs1, imp_finsts = finsts1 })
643 (ImportAvails { imp_mods = mods2,
644 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
645 imp_orphs = orphs2, imp_finsts = finsts2 })
646 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
647 imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,
648 imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
649 imp_orphs = orphs1 `unionLists` orphs2,
650 imp_finsts = finsts1 `unionLists` finsts2 }
652 plus_mod_dep (m1, boot1) (m2, boot2)
653 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
654 -- Check mod-names match
655 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
658 %************************************************************************
660 \subsection{Where from}
662 %************************************************************************
664 The @WhereFrom@ type controls where the renamer looks for an interface file
668 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
669 | ImportBySystem -- Non user import.
671 instance Outputable WhereFrom where
672 ppr (ImportByUser is_boot) | is_boot = ptext (sLit "{- SOURCE -}")
674 ppr ImportBySystem = ptext (sLit "{- SYSTEM -}")
678 %************************************************************************
682 These are forced to be in TcRnTypes because
683 TcLclEnv mentions WantedConstraints
684 WantedConstraint mentions CtLoc
685 CtLoc mentions ErrCtxt
688 v%************************************************************************
691 data WantedConstraints
692 = WC { wc_flat :: Bag WantedEvVar -- Unsolved constraints, all wanted
693 , wc_impl :: Bag Implication
694 , wc_insol :: Bag FlavoredEvVar -- Insoluble constraints, can be
695 -- wanted, given, or derived
696 -- See Note [Insoluble constraints]
699 emptyWC :: WantedConstraints
700 emptyWC = WC { wc_flat = emptyBag, wc_impl = emptyBag, wc_insol = emptyBag }
702 mkFlatWC :: Bag WantedEvVar -> WantedConstraints
703 mkFlatWC wevs = WC { wc_flat = wevs, wc_impl = emptyBag, wc_insol = emptyBag }
705 isEmptyWC :: WantedConstraints -> Bool
706 isEmptyWC (WC { wc_flat = f, wc_impl = i, wc_insol = n })
707 = isEmptyBag f && isEmptyBag i && isEmptyBag n
709 insolubleWC :: WantedConstraints -> Bool
710 -- True if there are any insoluble constraints in the wanted bag
711 insolubleWC wc = not (isEmptyBag (wc_insol wc))
712 || anyBag ic_insol (wc_impl wc)
714 andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
715 andWC (WC { wc_flat = f1, wc_impl = i1, wc_insol = n1 })
716 (WC { wc_flat = f2, wc_impl = i2, wc_insol = n2 })
717 = WC { wc_flat = f1 `unionBags` f2
718 , wc_impl = i1 `unionBags` i2
719 , wc_insol = n1 `unionBags` n2 }
721 addFlats :: WantedConstraints -> Bag WantedEvVar -> WantedConstraints
722 addFlats wc wevs = wc { wc_flat = wc_flat wc `unionBags` wevs }
724 addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
725 addImplics wc implic = wc { wc_impl = wc_impl wc `unionBags` implic }
727 instance Outputable WantedConstraints where
728 ppr (WC {wc_flat = f, wc_impl = i, wc_insol = n})
729 = ptext (sLit "WC") <+> braces (vcat
730 [ if isEmptyBag f then empty else
731 ptext (sLit "wc_flat =") <+> pprBag pprWantedEvVar f
732 , if isEmptyBag i then empty else
733 ptext (sLit "wc_impl =") <+> pprBag ppr i
734 , if isEmptyBag n then empty else
735 ptext (sLit "wc_insol =") <+> pprBag ppr n ])
737 pprBag :: (a -> SDoc) -> Bag a -> SDoc
738 pprBag pp b = foldrBag (($$) . pp) empty b
743 data Untouchables = NoUntouchables
747 -- A TcMetaTyvar is *touchable* iff its unique u satisfies
751 instance Outputable Untouchables where
752 ppr NoUntouchables = ptext (sLit "No untouchables")
753 ppr (TouchableRange low high) = ptext (sLit "Touchable range:") <+>
754 ppr low <+> char '-' <+> ppr high
756 isNoUntouchables :: Untouchables -> Bool
757 isNoUntouchables NoUntouchables = True
758 isNoUntouchables (TouchableRange {}) = False
760 inTouchableRange :: Untouchables -> TcTyVar -> Bool
761 inTouchableRange NoUntouchables _ = True
762 inTouchableRange (TouchableRange low high) tv
763 = uniq >= low && uniq < high
767 -- EvVar defined in module Var.lhs:
768 -- Evidence variables include all *quantifiable* constraints
770 -- implicit parameters
771 -- coercion variables
774 %************************************************************************
776 Implication constraints
778 %************************************************************************
783 ic_untch :: Untouchables, -- Untouchables: unification variables
784 -- free in the environment
785 ic_env :: TcTypeEnv, -- The type environment
786 -- Used only when generating error messages
787 -- Generally, ic_untch is a superset of tvsof(ic_env)
788 -- However, we don't zonk ic_env when zonking the Implication
789 -- Instead we do that when generating a skolem-escape error message
791 ic_skols :: TcTyVarSet, -- Introduced skolems
792 -- See Note [Skolems in an implication]
794 ic_given :: [EvVar], -- Given evidence variables
795 -- (order does not matter)
796 ic_loc :: GivenLoc, -- Binding location of the implication,
797 -- which is also the location of all the
798 -- given evidence variables
800 ic_wanted :: WantedConstraints, -- The wanted
801 ic_insol :: Bool, -- True iff insolubleWC ic_wanted is true
803 ic_binds :: EvBindsVar -- Points to the place to fill in the
804 -- abstraction and bindings
807 instance Outputable Implication where
808 ppr (Implic { ic_untch = untch, ic_skols = skols, ic_given = given
810 , ic_binds = binds, ic_loc = loc })
811 = ptext (sLit "Implic") <+> braces
812 (sep [ ptext (sLit "Untouchables = ") <+> ppr untch
813 , ptext (sLit "Skolems = ") <+> ppr skols
814 , ptext (sLit "Given = ") <+> pprEvVars given
815 , ptext (sLit "Wanted = ") <+> ppr wanted
816 , ptext (sLit "Binds = ") <+> ppr binds
817 , pprSkolInfo (ctLocOrigin loc)
818 , ppr (ctLocSpan loc) ])
821 Note [Skolems in an implication]
822 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
823 The skolems in an implication are not there to perform a skolem escape
824 check. That happens because all the environment variables are in the
825 untouchables, and therefore cannot be unified with anything at all,
826 let alone the skolems.
828 Instead, ic_skols is used only when considering floating a constraint
829 outside the implication in TcSimplify.floatEqualities or
830 TcSimplify.approximateImplications
832 Note [Insoluble constraints]
833 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
834 Some of the errors that we get during canonicalization are best
835 reported when all constraints have been simplified as much as
836 possible. For instance, assume that during simplification the
837 following constraints arise:
839 [Wanted] F alpha ~ uf1
840 [Wanted] beta ~ uf1 beta
842 When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail
843 we will simply see a message:
844 'Can't construct the infinite type beta ~ uf1 beta'
845 and the user has no idea what the uf1 variable is.
847 Instead our plan is that we will NOT fail immediately, but:
848 (1) Record the "frozen" error in the ic_insols field
849 (2) Isolate the offending constraint from the rest of the inerts
850 (3) Keep on simplifying/canonicalizing
852 At the end, we will hopefully have substituted uf1 := F alpha, and we
853 will be able to report a more informative error:
854 'Can't construct the infinite type beta ~ F alpha beta'
856 %************************************************************************
858 EvVarX, WantedEvVar, FlavoredEvVar
860 %************************************************************************
863 data EvVarX a = EvVarX EvVar a
864 -- An evidence variable with accompanying info
866 type WantedEvVar = EvVarX WantedLoc -- The location where it arose
867 type FlavoredEvVar = EvVarX CtFlavor
869 instance Outputable (EvVarX a) where
870 ppr (EvVarX ev _) = pprEvVarWithType ev
871 -- If you want to see the associated info,
872 -- use a more specific printing function
874 mkEvVarX :: EvVar -> a -> EvVarX a
877 evVarOf :: EvVarX a -> EvVar
878 evVarOf (EvVarX ev _) = ev
880 evVarX :: EvVarX a -> a
881 evVarX (EvVarX _ a) = a
883 evVarOfPred :: EvVarX a -> PredType
884 evVarOfPred wev = evVarPred (evVarOf wev)
886 wantedToFlavored :: WantedEvVar -> FlavoredEvVar
887 wantedToFlavored (EvVarX v wl) = EvVarX v (Wanted wl)
889 keepWanted :: Bag FlavoredEvVar -> Bag WantedEvVar
891 = foldrBag keep_wanted emptyBag flevs
892 -- Important: use fold*r*Bag to preserve the order of the evidence variables.
894 keep_wanted :: FlavoredEvVar -> Bag WantedEvVar -> Bag WantedEvVar
895 keep_wanted (EvVarX ev (Wanted wloc)) r = consBag (EvVarX ev wloc) r
901 pprEvVars :: [EvVar] -> SDoc -- Print with their types
902 pprEvVars ev_vars = vcat (map pprEvVarWithType ev_vars)
904 pprEvVarTheta :: [EvVar] -> SDoc
905 pprEvVarTheta ev_vars = pprTheta (map evVarPred ev_vars)
907 pprEvVarWithType :: EvVar -> SDoc
908 pprEvVarWithType v = ppr v <+> dcolon <+> pprPred (evVarPred v)
910 pprWantedsWithLocs :: WantedConstraints -> SDoc
911 pprWantedsWithLocs wcs
912 = vcat [ pprBag pprWantedEvVarWithLoc (wc_flat wcs)
913 , pprBag ppr (wc_impl wcs)
914 , pprBag ppr (wc_insol wcs) ]
916 pprWantedEvVarWithLoc, pprWantedEvVar :: WantedEvVar -> SDoc
917 pprWantedEvVarWithLoc (EvVarX v loc) = hang (pprEvVarWithType v)
919 pprWantedEvVar (EvVarX v _) = pprEvVarWithType v
922 %************************************************************************
926 %************************************************************************
930 = Given GivenLoc -- We have evidence for this constraint in TcEvBinds
932 -- We have evidence for this constraint in TcEvBinds;
933 -- *however* this evidence can contain wanteds, so
934 -- it's valid only provisionally to the solution of
936 | Wanted WantedLoc -- We have no evidence bindings for this constraint.
938 -- data DerivedOrig = DerSC | DerInst | DerSelf
939 -- Deriveds are either superclasses of other wanteds or deriveds, or partially
940 -- solved wanteds from instances, or 'self' dictionaries containing yet wanted
943 instance Outputable CtFlavor where
944 ppr (Given {}) = ptext (sLit "[G]")
945 ppr (Wanted {}) = ptext (sLit "[W]")
946 ppr (Derived {}) = ptext (sLit "[D]")
947 pprFlavorArising :: CtFlavor -> SDoc
948 pprFlavorArising (Derived wl ) = pprArisingAt wl
949 pprFlavorArising (Wanted wl) = pprArisingAt wl
950 pprFlavorArising (Given gl) = pprArisingAt gl
952 isWanted :: CtFlavor -> Bool
953 isWanted (Wanted {}) = True
956 isGiven :: CtFlavor -> Bool
957 isGiven (Given {}) = True
960 isDerived :: CtFlavor -> Bool
961 isDerived (Derived {}) = True
965 %************************************************************************
969 %************************************************************************
971 The 'CtLoc' gives information about where a constraint came from.
972 This is important for decent error message reporting because
973 dictionaries don't appear in the original source code.
977 data CtLoc orig = CtLoc orig SrcSpan [ErrCtxt]
979 type WantedLoc = CtLoc CtOrigin -- Instantiation for wanted constraints
980 type GivenLoc = CtLoc SkolemInfo -- Instantiation for given constraints
982 ctLocSpan :: CtLoc o -> SrcSpan
983 ctLocSpan (CtLoc _ s _) = s
985 ctLocOrigin :: CtLoc o -> o
986 ctLocOrigin (CtLoc o _ _) = o
988 setCtLocOrigin :: CtLoc o -> o' -> CtLoc o'
989 setCtLocOrigin (CtLoc _ s c) o = CtLoc o s c
991 pushErrCtxt :: orig -> ErrCtxt -> CtLoc orig -> CtLoc orig
992 pushErrCtxt o err (CtLoc _ s errs) = CtLoc o s (err:errs)
994 pprArising :: CtOrigin -> SDoc
995 -- Used for the main, top-level error message
996 -- We've done special processing for TypeEq and FunDep origins
997 pprArising (TypeEqOrigin {}) = empty
998 pprArising FunDepOrigin = empty
999 pprArising orig = text "arising from" <+> ppr orig
1001 pprArisingAt :: Outputable o => CtLoc o -> SDoc
1002 pprArisingAt (CtLoc o s _) = sep [ text "arising from" <+> ppr o
1003 , text "at" <+> ppr s]
1006 %************************************************************************
1010 %************************************************************************
1013 -- SkolemInfo gives the origin of *given* constraints
1014 -- a) type variables are skolemised
1015 -- b) an implication constraint is generated
1017 = SigSkol UserTypeCtxt -- A skolem that is created by instantiating
1018 Type -- a programmer-supplied type signature
1019 -- Location of the binding site is on the TyVar
1021 -- The rest are for non-scoped skolems
1022 | ClsSkol Class -- Bound at a class decl
1023 | InstSkol -- Bound at an instance decl
1024 | DataSkol -- Bound at a data type declaration
1025 | FamInstSkol -- Bound at a family instance decl
1026 | PatSkol -- An existential type variable bound by a pattern for
1027 DataCon -- a data constructor with an existential type.
1028 (HsMatchContext Name)
1029 -- e.g. data T = forall a. Eq a => MkT a
1031 -- The pattern MkT x will allocate an existential type
1032 -- variable for 'a'.
1034 | ArrowSkol -- An arrow form (see TcArrows)
1036 | IPSkol [IPName Name] -- Binding site of an implicit parameter
1038 | RuleSkol RuleName -- The LHS of a RULE
1040 | InferSkol [(Name,TcType)]
1041 -- We have inferred a type for these (mutually-recursivive)
1042 -- polymorphic Ids, and are now checking that their RHS
1043 -- constraints are satisfied.
1045 | BracketSkol -- Template Haskell bracket
1047 | UnkSkol -- Unhelpful info (until I improve it)
1049 instance Outputable SkolemInfo where
1052 pprSkolInfo :: SkolemInfo -> SDoc
1053 -- Complete the sentence "is a rigid type variable bound by..."
1054 pprSkolInfo (SigSkol (FunSigCtxt f) ty)
1055 = hang (ptext (sLit "the type signature for"))
1056 2 (ppr f <+> dcolon <+> ppr ty)
1057 pprSkolInfo (SigSkol cx ty) = hang (pprUserTypeCtxt cx <> colon)
1059 pprSkolInfo (IPSkol ips) = ptext (sLit "the implicit-parameter bindings for")
1060 <+> pprWithCommas ppr ips
1061 pprSkolInfo (ClsSkol cls) = ptext (sLit "the class declaration for") <+> quotes (ppr cls)
1062 pprSkolInfo InstSkol = ptext (sLit "the instance declaration")
1063 pprSkolInfo DataSkol = ptext (sLit "the data type declaration")
1064 pprSkolInfo FamInstSkol = ptext (sLit "the family instance declaration")
1065 pprSkolInfo BracketSkol = ptext (sLit "a Template Haskell bracket")
1066 pprSkolInfo (RuleSkol name) = ptext (sLit "the RULE") <+> doubleQuotes (ftext name)
1067 pprSkolInfo ArrowSkol = ptext (sLit "the arrow form")
1068 pprSkolInfo (PatSkol dc mc) = sep [ ptext (sLit "a pattern with constructor")
1069 , nest 2 $ ppr dc <+> dcolon
1070 <+> ppr (dataConUserType dc) <> comma
1071 , ptext (sLit "in") <+> pprMatchContext mc ]
1072 pprSkolInfo (InferSkol ids) = sep [ ptext (sLit "the inferred type of")
1073 , vcat [ ppr name <+> dcolon <+> ppr ty
1074 | (name,ty) <- ids ]]
1077 -- For type variables the others are dealt with by pprSkolTvBinding.
1078 -- For Insts, these cases should not happen
1079 pprSkolInfo UnkSkol = WARN( True, text "pprSkolInfo: UnkSkol" ) ptext (sLit "UnkSkol")
1083 %************************************************************************
1087 %************************************************************************
1090 -- CtOrigin gives the origin of *wanted* constraints
1092 = OccurrenceOf Name -- Occurrence of an overloaded identifier
1093 | AppOrigin -- An application of some kind
1095 | SpecPragOrigin Name -- Specialisation pragma for identifier
1097 | TypeEqOrigin EqOrigin
1099 | IPOccOrigin (IPName Name) -- Occurrence of an implicit parameter
1101 | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal
1102 | NegateOrigin -- Occurrence of syntactic negation
1104 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
1105 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
1107 | TupleOrigin -- (..,..)
1108 | ExprSigOrigin -- e :: ty
1109 | PatSigOrigin -- p :: ty
1110 | PatOrigin -- Instantiating a polytyped pattern at a constructor
1114 | ScOrigin -- Typechecking superclasses of an instance declaration
1115 | DerivOrigin -- Typechecking deriving
1116 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
1117 | DefaultOrigin -- Typechecking a default decl
1118 | DoOrigin -- Arising from a do expression
1119 | IfOrigin -- Arising from an if statement
1120 | ProcOrigin -- Arising from a proc expression
1121 | AnnOrigin -- An annotation
1126 { uo_actual :: TcType
1127 , uo_expected :: TcType }
1129 instance Outputable CtOrigin where
1130 ppr orig = pprO orig
1132 pprO :: CtOrigin -> SDoc
1133 pprO (OccurrenceOf name) = hsep [ptext (sLit "a use of"), quotes (ppr name)]
1134 pprO AppOrigin = ptext (sLit "an application")
1135 pprO (SpecPragOrigin name) = hsep [ptext (sLit "a specialisation pragma for"), quotes (ppr name)]
1136 pprO (IPOccOrigin name) = hsep [ptext (sLit "a use of implicit parameter"), quotes (ppr name)]
1137 pprO RecordUpdOrigin = ptext (sLit "a record update")
1138 pprO ExprSigOrigin = ptext (sLit "an expression type signature")
1139 pprO PatSigOrigin = ptext (sLit "a pattern type signature")
1140 pprO PatOrigin = ptext (sLit "a pattern")
1141 pprO ViewPatOrigin = ptext (sLit "a view pattern")
1142 pprO IfOrigin = ptext (sLit "an if statement")
1143 pprO (LiteralOrigin lit) = hsep [ptext (sLit "the literal"), quotes (ppr lit)]
1144 pprO (ArithSeqOrigin seq) = hsep [ptext (sLit "the arithmetic sequence"), quotes (ppr seq)]
1145 pprO (PArrSeqOrigin seq) = hsep [ptext (sLit "the parallel array sequence"), quotes (ppr seq)]
1146 pprO SectionOrigin = ptext (sLit "an operator section")
1147 pprO TupleOrigin = ptext (sLit "a tuple")
1148 pprO NegateOrigin = ptext (sLit "a use of syntactic negation")
1149 pprO ScOrigin = ptext (sLit "the superclasses of an instance declaration")
1150 pprO DerivOrigin = ptext (sLit "the 'deriving' clause of a data type declaration")
1151 pprO StandAloneDerivOrigin = ptext (sLit "a 'deriving' declaration")
1152 pprO DefaultOrigin = ptext (sLit "a 'default' declaration")
1153 pprO DoOrigin = ptext (sLit "a do statement")
1154 pprO ProcOrigin = ptext (sLit "a proc expression")
1155 pprO (TypeEqOrigin eq) = ptext (sLit "an equality") <+> ppr eq
1156 pprO AnnOrigin = ptext (sLit "an annotation")
1157 pprO FunDepOrigin = ptext (sLit "a functional dependency")
1159 instance Outputable EqOrigin where
1160 ppr (UnifyOrigin t1 t2) = ppr t1 <+> char '~' <+> ppr t2